The invention is directed to instrumental color readings and in particular to an apparatus that can consistently position a color sample in a plurality of fixed and repeatable positions with a uniform and repeatable force to enhance repeatability of color readings.
The use of portable color measurement instruments, such as spectrophotometers and calorimeters in the automobile manufacturing and automobile refinish paint industry for measuring the color of paint samples is well known.
The shading standards for automotive refinish paints have very close tolerances. The measured color of a sample, however, often varies if the position or angle of a color sample changes slightly in relation to the optics of a portable spectrophotometer. Another problem in the determination of color sample measurements is that the measured color value of a particular color sample may vary from one reading to another if the force with which the color sample and color measurement instrument are held together varies from reading to reading. Because color measurement instrument operators cannot consistently hold the color samples and color measurement instrument together with the same uniform force time after time, the measured colors of samples are subject to operator variability. Thus, different color measurement instrument operators may get different color measurements from the same sample, or an operator may get different measurements from a sample depending on the positioning of the sample with respect to the color measurement instrument optics and the force applied when the color reading is taken.
The color measurement of metallic paints is further complicated by the inherent non-uniformity of metallic finishes. Additionally, because the metallic flakes in metallic paints may be directionally oriented, they are subject to what is known as the xe2x80x9cVenetian blindxe2x80x9d effect, potentially causing the measured color or metallic paints to vary if the orientation of the sample changes in relation to the color measurement instrument. Because of the inherent non-uniformity and Venetian blind effect, refinish paint manufacturers will take multiple color measurements at different locations on a color sample, all measured with the same sample orientation, and combine those measurements to produce an averaged color measurement.
Variations in color readings caused by differences in the location on a color sample where a color measurement is taken, and the force applied by the color measurement instrument operator from one sample to another, or from one color measurement instrument operator to another for the same sample, may exceed the acceptable tolerances for the sample being measured. Thus, operator variability may produce false rejections or false acceptances of paint formulations. False rejections occur when a color sample that is actually within the acceptable color match tolerances is erroneously rejected. False acceptances occur when a color sample that is actually outside the color match tolerances is erroneously approved. Consistently positioning the color measurement instrument on the same spot on a sample, or for metallic paints on multiple spots, with a uniform and repeatable force is, therefore, essential to obtaining repeatable color readings, and thereby avoid false acceptances and false rejections.
Generally, the optics of a portable color measurement instrument is manually held against the surface of a color sample by the instrument operator. Manual positioning of a color measurement instrument in proximity to a color sample causes variation in color readings because the operator cannot consistently place the color measurement instrument on the sample in the same position and with the same force time after time. It is also generally known that a portable color measurement instrument and test sample can be secured in a fixture to obtain color measurements. Existing fixtures are available for holding a color measurement instrument and color sample but are subject to operator variability because the force with which a color sample is secured in the fixture varies from one operator to another. Moreover, existing holding fixtures do not permit a color measurement instrument operator to make multiple color readings at multiple, repeatable locations on a sample as is required for measuring metallic paint color values.
Automobile manufacturers and refinish paint manufactures experience problems similar to those noted above when using larger stationary color measurement instruments.
The refinish paint industry has a need for an apparatus that can consistently position a color sample in a plurality of fixed and repeatable positions in proximity with the optics port of either a portable or stationary color measurement instrument with uniform and repeatable force, thereby, eliminating color measurement instrument operator variability as a source of error in color readings by refinish paint manufacturing quality control personnel. Benefits accruing from increased repeatability and reproducibility of color measurements include savings from reduced or eliminated remixing of improperly mixed paint, and saving from reduced or eliminated costs of disposal of mixed paint that cannot be remixed.
The invention has the advantage over prior apparatus in that it provides color measurement instrument operators a means for quickly and consistently positioning color samples in multiple distinct and repeatable positions in relation to the optics port of a portable color measurement instrument, and holding the color sample in position with a uniform and repeatable force, thereby eliminating operator variability as a source of error when comparing color samples to known standards, or when measuring samples for future comparison with other samples.
While this invention can be used with all color measurement instruments, not just spectrophotometers and colorimeters, the invention is now described with reference to calorimeters, as these are the preferred instruments. The present invention is an apparatus for holding a generally flat color sample in juxtaposition with the optics port of a calorimeter, comprising a calorimeter support plate, a color sample stage defining an aperture capable of receiving the colorimeter optics shoe; a means for removably securing the colorimeter support plate to the calorimeter with the optics shoe engaged in the aperture; a means for positioning the color sample in a plurality of fixed and repeatable positions on the color sample stage wherein the optics port is disposed on a distinct location on the color sample in each of the positions, and the aperture is fully covered by the color sample in all positions; and a means for removably securing the color sample to the color sample stage with a uniform and repeatable force.